For a utility operating a nuclear reactor system, it is imperative that Inservice Inspection (ISI) of the reactor system welds be performed as rapidly as possible without sacrificing accuracy. The inspection system is comprised of mechanical locomotion equipment and nondestructive examination instrumentation. It is desirable to reduce the time in making these inspections without reducing the quality of the examinations. Reduction in this time will enable the utility to realize savings in operating costs due to shorter downtimes and a reduction in radiation exposure to examination personnel.
The present rules for ISI, established by the ASME Code, Section XI "Rules for Inservice Inspection of Nuclear Power Plant Components", require a complete inspection of reactor vessel and steam generator welds every ten operational years. In addition, it is a USNRC requirement that personnel radiation exposure be "as low as reasonably achievable." Hence, it is inevitable, based on these criteria and the very high cost of plant downtime, that an inspection agency must provide reliable, accurate, and rapid inspection techniques.
The inservice inspection program includes both the component and piping welds. In general, there are numerous access problems, weld configuration variations and radiation hazards that must be considered. The stay cylinder of the steam generator is vertically extended. The mounting structure for the ultrasonic transducers must be inserted within a convenient manway and remotely controlled to progress vertically up the length of the cylinder. It has been the practice to provide a permanent track structure internally of the cylinder on which the transducer mount may progress.
The prior art track requires moving parts which may, over long periods of time, become inoperative to some degree. After all, inspections are every 10 years and after 40 years, deterioration of the track, and moving parts associated with it, can be expected. If a platform, or support structure, can be provided for the ultrasonic inspection deck which can be inserted through the convenient manway, and progress up the internal surface of a cylindrical shaft, the inspection deck can be mounted thereon and be brought to its weld bodies requiring the inspection without reliance upon the mechanical complications of a track. There will be no sacrifice of positional precision. The platform, or support structure, will be actuated to progress by remote control and the intelligence from the transducers will be transmitted to the remote location for the personnel.
The specific problems of inspecting the vertical stay cylinder of the nuclear steam generator triggered awareness of the more broadly defined problem. Not only vertical stay cylinders may require inspection and other work at predetermined areas, but any passageway in tne nuclear reactor system has similar requirements. Further, the requirement of inspection and other work associated with pssageways with various cross-sectional configurations exist elsewhere other than the nuclear reactor systems. The progressed support structure for attached tools is demanded anywhere the elongated passageways require remote control to position working tools to specific areas along the passageways.